how can you create a histogram which outputs how many times a character appeared in a

[user959]

create a new class on JavaScript called “MyString” that computes a histogram representing the number of times each letter of the alphabet is in a given text.

[gits]

well - it looks like an assignment but i guess we can answer it now after a few months to help those that might find it through a search or such. a pretty quick and straight forward solution to that could look like this:

class TextHandler {
 
    constructor(txt) {
 
        if (typeof txt !== 'string') {
            throw 'cant create object - param has to be a string';
        }
 
        this.txt = txt;
    }
 
    __initList() {
 
        return {
            a:0, b:0, c:0, d:0, e:0, f:0, g:0,
            h:0, i:0, j:0, k:0, l:0, m:0, n:0,
            o:0, p:0, q:0, r:0, s:0, t:0, u:0,
            v:0, w:0, x:0, y:0, z:0
        };
    }
 
    get histogram() {
 
        let charHistogram = this.__initList();
 
        for (let i in charHistogram) {
 
            let re = new RegExp('([' + i + '])', 'gi');
            let ma = this.txt.match(re);
 
            charHistogram[i] = ma !== null ? ma.length : 0;
        }
 
        return charHistogram;
    }
}

it should fulfill the minimum requirements that can be read from the post - and it should be adapted to what the real! requirements would be.

PS: usage could look like:

new TextHandler('foobar').histogram;

PPS: since i now was interested :) it appears that such a task can be optimized much by using another approach that simply reduces the needed operations - so during every loop-step we could reduce the text by just replacing the already checked characters like that:

 
    get histogram() {
 
        let charHistogram = this.__initList();
        let txt = this.txt;
 
        for (let i in charHistogram) {
 
            let le = txt.length;
            let re = new RegExp('([' + i + '])', 'gi');
 
            txt = txt.replace(re, '');
 
            charHistogram[i] = le - txt.length;
        }
 
        return charHistogram;
    }
 

that made creating the histogram much faster with longer texts - i roughly measured 5x faster execution times with that method (text used for measurement had 21793 characters). note that this consumes the text we use for that - thats why i dont operate on it but assign it to a local variable - and the nice side effect would be that we can have an easy access to the residue at the end that we didnt count in - in the above case all characters like special chars or numbers and such (we count only whats in the initial list).

PPPS: could even be more optimized - probably slightly only but still - by ordering our counting map according to the common frequency of letters in a text in a language. i ordered the list according to here:

https://en.wikipedia.org/wiki/Letter_frequency

that squeezed out another few milliseconds per pass - was only noticable when i increased the text size though to 130758 characters. got roughly 15% faster execution times with it by just starting with the letter e and t instead of a and b.